The present invention concerns the field of power electronics. It relates to a parallel circuit comprising a plurality of IGBTs.
For a relatively long time power electronic semiconductor modules have been commercially available in which up to six high-power IGBTs with corresponding reverse-connected parallel diodes are arranged and interconnected in such a way that they can either form the individual arms of a three-phase power converter bridge or can be combined by being connected in parallel to form a single phase arm with three-fold current-carrying capacity. Modules of this type are offered by the applicant under the general type designation LoPak5 and have, by way of example, a collector-emitter voltage VCE of 1200 V and a collector current Ic of 300 A (see the data sheet 5SYA1528 from ABB Semiconductors AG relating to the module type 5SNS030OU120100 of Jul. 1, 2000).
The parallel circuit comprising such high-power IGBTs on the power side (i.e. by connecting the collector-emitter paths of the individual IGBTs in parallel) throws up various problems:
If the IGBTs with their associated gate drive circuits (xe2x80x9cgate drivesxe2x80x9d) are only connected in parallel on the power side without further measures, considerable unequal distribution of the currents between the individual IGBTs can occur dynamically due to different delays in the gate drive circuits during the switching of the IGBTs. Since the individual gates of the IGBTs are not connected to one another, the positive transistor behavior of the IGBTs does not help either.
If the gates of the IGBTs are likewise connected in parallel, the IGBTs, owing to their fundamental transistor behavior, naturally have the tendency to statically divide the currents identically among themselves: identical transistors have identical ICE/VCE characteristics and - since they have the same VCE and the same gate voltage - they must also draw the same collector-emitter current ICE. Dynamically, however, the currents can differ considerably. The absolute values of the gate resistances as well as the ratio of individual and common resistances in the module influence the balance between the currents.
The output stage of a gate drive circuit used for such IGBTs is usually a push-pull stage constructed with two MOSFETs (p-channel and n-channel MOSFETs). If two gate drive circuits are connected in parallel, it must be ensured that one gate drive circuit does not break down to the other and that one gate drive circuit does not xe2x80x9cchargexe2x80x9d the other. The simplest solution is to use individual gate resistors for decoupling the gate drive circuits. However, such a solution can only be realized for two gate drive circuits connected in parallel.
It is an object of the invention, therefore, to specify a parallel circuit comprising high-power IGBTs in which more than two gate drive circuits are connected in parallel.
The essence of the invention is that the MOSFETs in the output stages of the gate drive circuits are in each case connected to a positive or negative supply terminal via a constant-current source and the outputs of the gate drive circuits are interconnected via a connecting line. In this case, the constant-current sources are designed as xe2x80x9cweakxe2x80x9d constant-current sources and are constructed in a manner known per se from a transistor or MOSFET and diodes and/or resistors.
In order that the power supplies of the gate drive circuits are at least uniformly loaded, it is advantageous if the positive and negative supply terminals of the gate drive circuits are respectively interconnected by connecting lines.